The present invention relates generally to transducer horn assembly debubbling devices and, more particularly, to methods and apparatus for measuring the electrical and mechanical characteristics of a transducer horn assembly and for determining the effectiveness of the transducer horn assembly in debubbling operations.
There are a variety of emulsions, suspensions, pastes and high viscosity liquids used in the manufacture or which become part of the variety of products in the chemical, pharmaceutical, food products, and photographic industries. These emulsions, suspensions, pastes and high viscosity liquids often contain air or gases which are dissolved therein or are present in the form of small bubbles. Often this air or gas, particularly in the case of entrained bubbles, is detrimental to the final product being produced. For example, in the case of photographic emulsions, the gas bubbles greatly impair the quality of the films or photographic papers produced with these emulsions because the bubbles disturb the evenness of volumetric flow of the emulsion as it is applied by the coating devices. This gives rise to the formation of streaks and spots making the photographic materials unusable.
An apparatus which is typically used in the photographic industry for debubbling photographic emulsions is an end cap round ultrasonic bubble eliminator, typically referred to as an ECR. The ECR includes a transducer horn assembly (hereinafter referred to as a xe2x80x9cTHAxe2x80x9d) which is an electromechanical device which converts electrical vibration to mechanical vibration. One particular ECR with its component THA is taught in U.S. Pat. No. 5,373,212 to Beau. In the operation of an ECR, an alternating voltage is applied to the ceramic disk of the THA which, as a result, generates mechanical vibration. This mechanical vibration results in the debubbling of the photographic emulsions flowing through the ECR.
The effectiveness and efficiency of an ECR THA in the performance of debubbling operations can be critical to whether or not an acceptable final product is produced. In the past there has been no practical method for testing the effectiveness and efficiency of an ECR THA and, therefore, an ECR THA which was no longer performing adequately was not replaced or repaired until it had resulted in the production of product which was out of specification or otherwise not useful. As a result, a means of testing the effectiveness and efficiency of the ECR THA was needed. Preferably, testing of the ECR THA could be performed on-line.
It is, therefore, an object of the present invention to provide a method and apparatus for testing ECR THA""s to determine and to predict the debubbling efficiency of the ECR itself.
A further object of the present invention is to provide a method and apparatus for testing an ECR THA""s which can be performed at either low or high power with the ECR off-line.
Still another object of the present invention is to provide a method and apparatus for testing ECR which can be performed with the ECR operating on-line.
Briefly stated, these and numerous other features, objects and advantages of the present invention will become readily apparent upon a reading of the detailed description, claims and drawings set forth herein. These features, objects and advantages are accomplished by making electrical measurements on the ECR THA and using those measurements to characterize the physical condition of the piezoelectric ceramics of the THA. In order to make electrical measurements on an ECR horn, it is necessary to measure the voltage and current drive signals. Since the ECR operates at high frequencies, nominally 40 kHz, an accurate alternating current measurement is required. The measurement must have a band width sufficient to maintain the fidelity of the signals and it must preserve the phase relationship between the voltage and current signals. A test box is connected between the ECR and a signal analyzer. The test box contains an electrical circuit which includes a current transformer in the supply leg of the drive signal being supplied to the horn, and a high impedance voltage divider between the supply and return legs. The current transformer provides an output voltage that is proportional to the current in the supply leg. The voltage divider provides a voltage signal that is {fraction (1/100)}th of the drive voltage. Capacitors are added to the circuit to compensate for stray capacitance in the voltage divider that can lead to unwanted phase shifts between the output of the voltage divider and the signal supplied to the current transformer. By making these measurements, an impedance trace can be generated for the horn. This impedance trace is compared to a model impedance trace. The model impedance trace has been developed for the purpose of understanding and predicting the performance of ECR THAs. Impedance measurements made directly on the ECR THAs have been used to confirm the model. Through the comparison of the impedance trace made for a particular ECR with the model, it can be determined whether the ECR is operational, that is, whether it is in good condition or damaged. Further, if the ECR is in working condition, the impedance trace can be used to determine how efficiently the ECR is operating. In this manner, an ultimate determination of how well a particular ECR is functioning as a debubbler can be made.